The effects of cigarette smoke on the intestinal and oral floras in mice were studied by gavage treatment with smoke extract and passive smoking treatment. The results showed that: comparing with the control group, the colony number of intestinal lactobacilli and bifidobacteria was significantly reduced (P<0.05) for gavage treatment group; however, there was no significant difference in the number of E. coli colonies; the colony number of oral Streptococcus mutans increased significantly (P<0.05). Comparing with the blank group, there was no significant difference in the number of intestinal lactobacilli, bifidobacteria and E. coli colonies for passive smoking group, however oral colony number of Streptococcus mutans increased significantly (P<0.05). The results revealed that gavage treatment with smoke extract destroyed the balance within intestinal floras and within oral floras, while passive smoking treatment only destroyed the balance within oral floras in mice.